“When you have a grassland, the plants living there convert the sun’s energy into leaf and root in roughly equal amounts. When the ruminant [e.g., a cow] comes along and grazes that grassland, it trims the height of the grass from, say, 3 feet tall to 3 inches tall. The plant responds to this change by seeking a new equilibrium: it kills off an amount of root mass equal to the amount of leaf and stem lost to grazing. The [discarded] root mass is then set upon by the nematodes, earthworms and other underground organisms, and they turn the carbon in the roots into soil. This is how all of the soil on earth has been created: from the bottom up, not the top down.”

A biologist named Allan Savory, in this fascinating TED talk, shows how bringing grazing animals to desert lands can bring back the plants.